I've got a problem with my VM 38mm Mikuni.
It's on my 1978 1000.
Does someoneknow this carb?
My question is concerning the needle jet.
Should it have a "P" or "B" type needle jet?

I need some help here...

Rick

 

From what I can determine your VM38 needs a 'P' type needle jet. As you probably know, the P stands for Primary Choke Type and the B stands for Bleed Type. The P type is almost straight sided, where the B type has a large barrel at the bottom and a washer like flange at the top. You should be able to see which shape yours is.
This jet leads fuel into the main jet and works in conjunction with the needle. The range this jet controls is between 1/4 and 3/4 throttle. Fuel control below 1/4 throttle is handled by the low speed jet, and above 3/4 throttle is by the main jet.

What kind of troulbe are you having? What makes you think the needle jet is the issue? If the Mikuni you have is the round slide type of carb, good luck finding any parts for it. I have called and talked with Mikuni directly and they do not have so much as a gasket kit available for the 38mm. I take very good care of the parts in mine for that reason..........pg

edit note: Do you have a better description of your carb? Model number perhaps?

 

The issue is, I opened-up the carb and there is not a needle jet. [:@]

I've actually read-up on the carb and realized why my bike hasn't run worth a damn.
I thought I needed a "P" type needle jet.

What I have is a "right-side" adjustment with the main jet in the front (nearest the air cleaner.)

 

Ironhead.......
Here are some pics of my 38mm Mikuni. Does yours look the same? I have a Mikuni Manual showing different part numbers for the many different model Mikuni carbs. I just need to know what model you have. I am not even sure what model mine is as I bought it in 1973, but I do know that parts are no longer available for it, as of the year 2000..........pg


[IMG]local://upfiles/8331/CD24E33462F849F3AB2BF7544FD44636.jpg[/IMG]

[IMG]local://upfiles/8331/038BE81D008147C9B2512F448F2FF278.jpg[/IMG]

[IMG]local://upfiles/8331/42B2758C94E646F3995A6BE7D3D23B46.jpg[/IMG]

 

PG, mine is very simular, from what I see.
Reading the 3-4's plugs: Black and soot covered. Cold plug, too lean?
What's weird, there's no needle jet.
What I found yesterday, the e-clip was set in the last groove (nearest the needle point.)
I moved it to the center groove and re-adjusted some more.

I know it's a booger trying to find out exactly what I have.

 

Ironhead......
Let me dig my Mikuni out of storage in the shop. I will take it apart and see what things are set at. As I remember my needle is in the middle position. I will pull the needle jet as well and prehaps take a pic of it to show you.
I have not had it apart in over 6 or 7 years, so I forget the details. Will try to get back to you today on that.......pg

edit note: The bottom setting is going to make things run rich (the needle is further out of the main jet). If you have black sooty spark plugs.....the plugs are too cold or the mixture is too rich, not lean. Number 3 and 4 plugs are OK, with 3 being the colder of the two. I am sure it is an over rich condition and dropping the needle to the middle position is going to help greatly.

 

Ironhead.....
Here is what I found:
My carb is a VM38-9 (38mm Mikuni)
It has a #330 main jet
It has a #30 pilot jet
It has a #166 Q2 needle jet
It has a 6DP1 needle......with the clip in the third notch from the top (middle notch)
The throttle valve (slide) is a VM38/24 2.5

My carb (and no doubt yours) has a main jet extender which screws into the bottom of the needle jet. The main jet then screws into the extender.
I have provided pic's of this. Hope this helps you some.
I assume you have the Mikuni website.....if not, then it is www.sudco.com
Let me know if this helps any........pg


[IMG]local://upfiles/8331/5599B627D2C6428286DC14313D63FB52.jpg[/IMG]

[IMG]local://upfiles/8331/91FE1CE1503C46E28C508B3563EF4540.jpg[/IMG]

[IMG]local://upfiles/8331/0A3C5D5CBDC8467D9546C6772415C031.jpg[/IMG]

 

Pics are worth a thousand words!
I'll jot-down on paper what part #'s I have.


I feel like I'm getting closer to figuring this booger out!

Thanks PG!

 

Here is one more view of the top of the needle jet. If you remove your slide and needle, this is the next thing you should see. I could not get the needle jet out of my carb easily, so I decided not to force anything and just took the shots in place.......pg

[IMG]local://upfiles/8331/FDCAE1A4822D458687B182CF0DCA8F7C.jpg[/IMG]

 

Piniongear/Ironhead...I have an original parts manual from Sudco/Mikuni published by Sudco Int Corp in 1975. Would it help any to copy it and get it to you? Think I can download and save it as a pdf file and email to you. Thouht I had an old 38 Mikuni as well but Im an not sure anymore. Will go through my stash of old parts.

And...got looking at the manual and it lists two VM-38s

VM 38-2 (38mm)part #size
main jet 4/042 #330
pilot jetVM22/210#35
needle jet166P-8
throttle valveVM38/022.5
air jetBS30/971.0
needlevalveVM34/393.3
needle6DP1-3

VM38-3 (38mm)
main jet 4/042 #360
pilot jet VM22/210 #50
neelde jet 166 P6
throttle valve VM38/02 2.5
air jet BS30/97 1.0
needle valve VM34/39
needle6DP1-3